CO2 (carbon dioxide) has been identified as a main greenhouse gas, CCS (carbon capture and storage) is considered as one of the potential major means to reduce the release of greenhouse gases into the atmosphere and to control global warming. In this context CCS is defined as the process of CO2 capture, compression, transport and storage. Capture is defined as a process in which CO2 is removed either from the flue gases after combustion of a carbon based fuel or the removal of and processing of carbon before combustion. Regeneration of any absorbents, adsorbents or other means to remove CO2 from a flue gas or fuel gas flow is considered to be part of the capture process.
Backend CO2 capture or post combustion capture is a commercially promising technology for fossil fuelled power plants including CCPP (combined cycle power plants). In backend capture the CO2 is removed from a flue gas. The remaining flue gas is released to the atmosphere and the CO2 is compressed for transportation, and storage. There are several technologies known to remove CO2 from a flue gas such as absorption, adsorption, membrane separation, and cryogenic separation.
Besides the energy required to remove the CO2 from flue gases, the energy required for CO2 compression is significant. To minimize the performance penalties due to CO2 compression the use of steam turbines to drive the CO2 compressors has been suggested. However, they rely on the availability of sufficient amounts of live steam. This steam is not available during the start-up and/or part load operation of a power plant. Depending on the type of power plant, it takes considerable time until steam is available. For a more flexible CO2 compressor operation the CO2 compressors are therefore typically powered by electric motors. These increase the operational flexibility but lead to additional expenses, losses in power and efficiency for generators and motors.